Generally, since signal transceiving is performed via a direct link between a fixed base station and a mobile station in a wireless communication system, it is facilitated to configure a highly-reliable wireless communication link between a base station and a mobile station. Yet, since a location of a base station may be fixed in a wireless communication system, a wireless network configuration is less flexible. Moreover, in a wireless environment having a considerable fluctuation of traffic distribution or call demand level, it is difficult to provide an efficient communication service. In order to overcome these disadvantages, it is able to apply a multi-hop type data transfer scheme to a general cellular wireless communication system using a fixed relay station, a mobile relay station or general mobile stations.
FIG. 1 is an illustrating diagram of network which performs the wireless communication using the relay station.
Referring to FIG. 1, a wireless communication system, which adopts a multi-hope relay scheme, is able to reconfigure a network to promptly cope with a communication environment change and is also able to operate and manage an overall wireless network more efficiently.
For instance, a wireless communication system, which adopts a multi-hop relay station scheme, extends a cell service area and increases a system capacity. In particular, if a channel status between a base station and a mobile station is poor, it is able to provide mobile station with a wireless channel having a better channel status by configuring a multi-hop relay station path via a relay station by establishing the relay station between the base station and the mobile station. Moreover, by applying a multi-hop relay station scheme to a cell boundary area having a poor channel status from a base station, it is able to provide a faster data channel and it is also able to extend a cell service area.
A relay station is the technology introduced for eliminating a radio wave shadow area in a mobile communication system and is widely used. Compared to an old system which is limited to a repeater function of transmitting a signal by simply amplifying the signal, a current system has evolved into a more intelligent system.
Moreover, a relay station technology is mandatory for a next generation communication system to reduce a cost for an extension of base station installations and a maintenance cost of a backhaul network and is also mandatory for a service coverage enlargement and a data processing rate improvement.
Next, a method of requiring uplink resources of a mobile station belonging to a relay station according to a related art is explained referring to FIG. 2. According to a related art, a mobile station belonging to a relay station requires uplink resources in the same way as a mobile station belonging to a base station.
OFDM physical layer specifies ranging subchannel and ranging code used for contention based bandwidth request. A mobile station selects a ranging code among a subset of ranging codes for bandwidth request to request bandwidth. A mobile station modulates the selected range code on the ranging subchannel and transmits it during a slot selected randomly from ranging area of a frame.
A base station detecting a ranging code allocates resources to a mobile station using CDMA allocation information element (IE) and connention identifier (CID), wherein the CDMA allocation IE specifies the ranging code the mobile station transmitted and transmission area in which the ranging code was transmitted. The mobile station transmits a signaling header or a grant management subheader, wherein the signaling header and the grant management subheader are includes bandwidth a request header and a bandwidth request field.
FIG. 2 illustrates signaling headers which a mobile station transmits to request uplink resources. FIGS. 2(a) illustrates a signaling header for bandwidth request, 2(b) illustrates a signaling header for bandwidth request and CINR report, 2(c) illustrates a signaling header for bandwidth request and uplink transmission power report, and 2(d) illustrates a signaling header for bandwidth request and uplink sleep control. Table 1 shows a grant management sub_header.
TABLE 1LengthName(bit)DescriptionFLI1Frame latency indication0 = FL field disabled for this grant1 = FL field enabled for this grantFL4Frame latency. The number of frames previous to the current one inwhich the transmitted data was available. When the latency is greaterthan 15 then the FL field shall be set to 15.Extended11The number of bytes of UL bandwidth requested by the MS. The BR isPiggybackfor the CID. The request shall not include any PHY overhead. In case ofRequestExtended rtPS, the BS changes its grant size to the size specified in thisfield.PBR16Piggyback request. The number of bytes of UL bandwidth requested bythe SS. The BR is for the CID. The request shall not include any PHYoverhead. The request shall be incremental.PM1Poll me 0 = No action 1 = Used by the SS to request a bandwidth poll.Reserved9—SI1Slip indicator 0 = No action 1 = Used by the SS to indicate a slip of ULgrants relative to the UL queue depth.
Or, a mobile station can transmits data through allocated resources.
According to a related art, in case that a relay station cannot be allocated uplink resource from a base station or a super relay station (super-RS) and its buffer is full when receiving uplink resources request from a sub-relay station (Sub-RS) or a mobile station, it cannot allocates resources to the Sub-RS or the mobile station within a period for which the mobile station waits for a response.
Then, if the mobile station does not be allocated uplink resources within the period, it retransmits an uplink resources request to the relay station. Thus, uplink signaling overhead is increased because of the retransmission of the uplink resources request.
A mobile station transmits a ranging request message including a base station identifier (BSID) of a serving base station to a target base station during handover procedure. So, a mobile station belonging to a relay station includes a BSID or a relay station identifier (RSID) in a ranging request message. A mobile station must know a BSID to include a BSID in a ranging request message. Or, when a mobile station includes a RSID in a ranging request message, a target base station have to know that an ID in a ranging request message is a RSID.